1. Field of the Invention
This invention relates to an array type light emitting element module, and particularly, to the configuration of a new light emitting element module capable of outputting laser beams of a plurality of desired types of oscillation wavelengths at the same time.
2. Description of the Related Art
There is a WDM (wavelength division multiplex) method for enabling higher-speed and higher-density data transmission using light signals. In this method, light signals which are different in wavelength are superposed on each other for transmission on one light transmission line, whereby the transmission density can be improved efficiently.
The WDM method requires for one to use a plurality of laser light sources which are different from each other in oscillation wavelength. Then, a plurality of light emitting element modules comprising DFB (distributed feedback) lasers, DBR (distributed bragg reflector) lasers, etc., which are different in oscillation wavelength are provided and the light waves of laser beams emitted from the semiconductor modules are combined by a light wave combiner for generating transmission light.
However, in order to form light sources for the WDM transmission system by the method as described above, it is difficult to complete light emitting element modules of predetermined oscillation wavelengths required for WDM transmission design. Since the light emitting element modules must be assembled separately and be furthermore combined, the number of manufacturing steps is increased resulting in an increase in cost.
Further, since the conventional WDM light source is provided by combining separately manufactured light emitting element modules, it is extremely difficult to miniaturize the WDM light source as a final product. In contrast, already known is a light emitting element module, as shown in FIG. 9, comprising a plurality of semiconductor lasers and a plurality of optical fibers integrally combined mainly for the purposes of high-density packaging and cost reduction. This light emitting element module consists of a light emitting element array 10 comprising a plurality of light emitting elements arranged on one row, an optical fiber array 20 comprising a plurality of optical fibers 2 placed on one array plane in parallel, and a common board 30 on which the light emitting element array 10 and the optical fiber array 20 are mounted. In fact, this type of light emitting element module further has an optical element 40 of lenses, etc., inserted between the light emitting face of the light emitting element array 10 and the incident end face of the optical fiber array 20 for enhancing the coupling efficiency of the light emitting elements 1 and the optical fibers 2.
However, in the conventional light emitting element module including a plurality of light emitting elements and optical fibers as described above, the light emitting elements 1 contained in the light emitting element array 10 have the same light emitting wavelength and cannot be used as a WDM light source requiring light signals which are different in wavelength. That is, the conventional light emitting element module can be only applied to simple parallel light transmission.